A supermarket is interested in finding out whether the mean weekly sales volume of Coca-Cola are the same when the soft drinks are displayed on the top shelf and when they are displayed on the bottom shelf. Ten stores are randomly selected from the supermarket chain with 5 stores using the top shelf display and 5 stores using the bottom shelf display. Assume that the samples are normally distributed with equal population variances. Refer to the sales volume data in the table below to answer the following:

1-What are the critical values using a level of significance alpha=.01?

2-what is the number of degree of freedom?

Top Shelf Sales Volume: 23 35 50 68 32

Bottom Shelf Sales Volume: 55 70 72 51 63